The purpose of this project is to determine if the use of premature chromosome condensation (PCC) technique will improve the resolution of the lymphocyte biological dosimetry system for low total doses of radiation (less than 1n rad). With the PCC technique, chromosomal damage (gross breaks in chromosomes) of interphase cells can be studied immediately following radiation exposure. Assays will be made before the cells have had time to repair many of the initial breaks, thereby increasing the number of breaks counted as opposed to counting aberrations conventionally 24-48 hours after exposure in metaphase I and II.